Cation Exchange Membrane with Internal-Blocking Sites for Mono/Multivalent Ion Separation

In this work, monovalent cation perm-selective membranes (MCPMs) with multiple internal-blocking sites were designed to enhance the Donnan effect and size-based exclusion effect. Polypyrrole (PPy), as the internal-blocking sites for ion transport, was introduced within the membrane matrix by in situ polymerization, which was prominent to mono- and multivalent ion separation in electrodialysis (ED). The precise growth of the internal-blocking sites was manipulated via optimization of the polymerization time and polymerization steps. The optimized SPPSU@3PPy membrane exhibits excellent separation performance: the SPPSU@3PPy membrane demonstrates perm-selectivity for Na+/Mg2+ (PNa Mg = 2.08) and a higher Na+ flux (JNa+ = 3.29 × 10–8 mol cm–2 s–1). This in situ polymerization method to fabricate internal-blocking sites in a cation exchange membrane is a potential pathway to construct MCPMs.